1. Field of the Invention
The invention relates to a control system for an inverter, and more particularly to a control system for an inverter constituted by six transistors and six diodes.
2. Description of Related Art
An apparatus that executes three-phase ON control when a short-circuit fault occurs in an inverter so that a switching element in which the short-circuit fault has occurred and switching elements connected in parallel thereto are all switched ON has been proposed as a conventional control system for an inverter of this type (see Japanese Patent Application Publication No. 2009-195026, for example). In this apparatus, when the inverter is short-circuited and a rotation speed of a motor/generator that is driven by the inverter is at or below a predetermined reference rotation speed, limp-home travel control is performed after switching ON the switching element in which the short-circuit fault has occurred and a switching element connected in series thereto. When the rotation speed of the motor/generator exceeds the predetermined reference rotation speed, on the other hand, the three-phase ON control is executed. In so doing, limp-home travel is performed while preventing an overcurrent from passing through the inverter.
In the control system for an inverter described above, however, a diode connected in parallel to the switching element in an opposite direction thereto may break.
When a diode through which a forward direction current is passed receives a voltage in an opposite direction at the start of the three-phase ON control, a recovery current (a reverse recovery current) passes through the diode. When the reverse direction voltage is too high or the recovery current is too large at this time, recovery loss may occur in excess of a recovery tolerance, and as a result, the diode may break.